Tee-nut insertion machines are in wide use for inserting Tee-nuts into a wooden workpiece. Such Tee-nuts usually comprise a sleeve portion which is internally threaded, and a face flange portion, which usually has prongs formed integrally therewith. In most cases the wooden workpiece is first of all predrilled on a drill press, and the wooden workpiece, already drilled, is then brought to the Tee-nut insertion machine. At that machine, each hole must be carefully registered with a Tee-nut insertion rod. The rod then picks up a Tee-nut and forces it into the predrilled hole. The rod at the same time forces the prongs into the workpiece around the hole.
Tee-nut machines, for this purpose, have been known in the past. In many cases the Tee-nuts were located loose in a hopper, and were fed downwardly to the lower end of a rod, which was, in fact, the piston rod of an operating cylinder.
The wooden workpiece was placed below the rod on an anvil, in registration with the Tee-nut. When the cylinder was operated, the hammer or piston rod would drive downwardly picking up the Tee-nut and forcing it into the hole.
In other machines, the cylinder and rod were located below the workpiece, and an anvil was located above the workpiece. In this case, the wooden workpiece was held upwardly against the anvil, with the hole registering with the Tee-nut which was located beneath it.
Operation of the cylinder would then pick up the Tee-nut and drive the Tee-nut upwardly into the workpiece.
Substantial improvements on these two types of machines are disclosed in U.S. Pat. No. 5,214,843, granted Jun. 1, 1993 inventors Walter H. Leistner and Keith G. Bromley, title "Fastener Setting Apparatus and Method and Fastener Strip Therefor", assignee Sigma Tool & Machine.
In that application, there is disclosed an arrangement of Tee-nuts, formed together into a strip by a flexible connection means. Tee-nuts could then be formed into a large roll. The roll could be placed on a table which was then fed to the insertion rod.
This system did away with the difficulties involved in handling loose Tee-nuts in a hopper, and considerably simplified the machine.
Such strips of Tee-nuts were applicable both to the upward insertion type of machine and also the downward insertion type of machine.
However, even using these improved machines, it was still necessary to predrill all of the Tee-nut holes on a drill press before the Tee-nuts could be inserted by the rod and cylinder.
Clearly, from the viewpoint of speed of operation, it would be desirable if the drilling step were eliminated. In the past, in connection with other types of fastenings, used in relatively thin members such as synthetic plastic panels, it has been the practice to both punch an opening through the thin workpiece and at the same time embed a fastening in the opening. The fastening was almost as long as the thickness of the plastic, and effectively punched out a slug of plastic, as the fastening was driven in. However, it was never thought practical or even possible to apply a self-punching technique to the insertion of Tee-nuts in thicker wooden workpieces. Tee-nuts are usually inserted in relatively thick wooden workpieces such as the frames of beds and furniture, or for example, in panels of shelving or other items of furniture. In some cases the wooden workpieces are both thick and made of softwood, and in other cases the workpieces may be made of hardwood, or chip board, or variations on chip board which are both more dense and stronger than conventional chip board.
In these cases, the workpiece is thicker than the length of the sleeve of the Tee-nut. It is necessary, in this cases, that the hole receiving the Tee-nut shall pass completely through the workpiece. This ensures that any male threaded fastening member which is inserted into the Tee-nut can extend completely through the sleeve, and into the hole in the workpiece, so as to permit the threads to be tightened up. In a typical bed frame or furniture frame, the wooden workpiece may be substantially thicker than the length of the Tee-nut. The Tee-nut sleeve may have a length of about one-half inch, more or less, depending upon the design of the Tee-nut.
It was always thought necessary in this application, that the holes must be pre-drilled. However, pre-drilling of holes, in a factory, on high speed drill presses, did not produce a clear, clean hole. Wood chips were usually left in the hole, and sometimes interfered with the Tee-nuts.
However, if it is attempted to punch a hole simultaneously with the driving of a Tee-nut into a workpiece of this thickness, it is necessary that the operation shall not only punch a hole of sufficient depth to receive the Tee-nut, but shall also punch a hole completely through the workpiece, even though the Tee-nut only reaches perhaps no more than one-half the thickness of the workpiece.
It is also desirable that the self-punching insertion machine shall be adaptable to Tee-nuts of various sizes, having sleeves of various different lengths, and also to workpieces of different thicknesses.
It is also apparent that in order to achieve this type of self-punching operation satisfactorily that the working cylinder must develop very substantial forces on the insertion piston rod. This in turn leads to considerations of the construction of the overall machine, and also safety considerations.
It is also necessary to ensure that in the punching operation, the sleeve of the Tee-nut does not become full of wood chips, since if it does, it may be difficult if not impossible to insert a male threaded member.
Thus the earlier problems relating to pre-drilling leaving wood chips, would not be solved.
The characteristics of the Tee-nuts themselves will also have a considerable influence on the operation of the machine, and all of these factors must be taken into account to produce a satisfactory, reliable machine capable of repetitively punching and simultaneously inserting Tee-nuts into a workpiece.
Still another problem in the design of such a machine is that it must be adaptable to workpieces of different types of woods some of which are softer and some of which are harder. The machine itself must be capable of being so adjusted that it will insert the Tee-nut to the correct depth in the workpiece, regardless of whether the workpiece is hard or soft. Under-insertion of the Tee-nut will be totally unacceptable, since a substantial portion of it will be left outside the workpiece. Over-insertion, for example in a softer workpiece, is equally undesirable, since it tends to damage the workpiece. The construction and design of such a machine must therefore take into account all of these varying conflicting factors, and solve them in a manner which is practical and satisfactory, and workable on the factory floor, as well as in the design laboratory.